Screw compressor with capacity control



Sept. 8, 1970 E, J. KOCHER ET AL 3,527,548

SCREW COMPRESSOR WITH CAPACITY CONTROL Filed April 10, 1969 3 Sheets-Sheet l r M 74 20 /& 5

\NVENTOZS E.J. Koause 3 Q0 24 w GER/v7- ATTORNEY,

Sept. 8, 1970 E. J. KOCHER ETAL 3,527,548

SCREW COMPRESSOR WITH CAPACITY CONTROL Filed April 10, 1969 3 Sheets$heet 2 ENTOES E. \J. ocHER w. Gee/v1 BY M 4 71%.

ATTOENEYS Sept. 8, 1970 KOCHER ET AL 3,527,548

I SCREW COMPRESSOR WITH CAPACITY CONTROL Filed April 10, 1969 5 Sheets-Sheet 5 f9? X r z v 0 mvENToe$ 7 4 4 M E. J. Koaqz W. G-EFVNT 1 BY $41,8 1 wee.

AT IO RNEYS United States Patent 3,527,548 SCREW COMPRESSOR WITH CAPACITY CONTROL Erich J. Kocher, Milwaukee, and Whitney I. Grant,

Muskego, Wis., assignors to Vilter Manufacturing Corporation, Milwaukee, Wis., a corporation of Wisconsm Filed Apr. 10, 1969, Ser. No. 815,172 Int. Cl. F04c 29/08, 17/12 US. Cl. 417-310 Claims ABSTRACT OF THE DISCLOSURE A screw compressor having means for controlling the capacity thereof to variable extents dependent upon the demand and for unloading the compressor during periods of no demand.

BACKGROUND Various types of compressors for operating on air or gas have heretofore been proposed. Among such machines is one which is commonly referred to as a screw type compressor. Generally speaking, such compressors comprise a pair of cooperating rotors, one male and one female, having intermeshing helical lobes or lands and intervening grooves or valleys for compressing the elastic fluid.

While these screw type compressors have been known to possess various advantages, perhaps the most noteworthy of which is smoothness and quietness in operation, they have nevertheless been relatively slow in becoming popular and have only recently enjoyed an appreciable degree of commercial success and acceptance. Probably the main reason for this relative slowness of acceptance has resided in the apparent lack of flexibility of this type of compressor and the inability to provide the machine with a simple and economical capacity control mechanism.

Even now, while this type of compressor is presently enjoying widespread acceptance in the air compressor industry, the universal acceptance thereof in the refrigeration industry has been undesirably limited, primarily due to the fact that the structures thus far proposed have not been modified for the etficient handling of gaseous refrigerants.

SUMMARY It is, therefore, an important object of the present invention to provide a screw type compressor with highly efficient capacity control and unloading means rendering the same extremely flexible in its adaptability and performance.

Another object of this invention is to provide improvements in the capacity control and unloading of screw type compressors which results in an extremely efficient machine which is readily adaptable for use with air or gas such as used, for example, in the refrigeration industry.

Still another object of the invention is to provide an improved screw type compressor having means for effecting capacity control and unloading which is extremely simple and compact in construction, efiicient and exacting in operation, and which may be readily embodied in a machine at relatively low cost and with only minor refinements to available apparatus.

A further object of the present invention is to provide an improved screw compressor of the type having cooperating male and female rotors with capacity control and unloading means by porting the grooves or valleys between the intermeshing lobes or lands to exhaust through either the hollow rotor hubs or hollow vanes, the volume of gas lay-passed through the ports in the rotors being controlled by a valve axially movable along the rotor Patented Sept. 8, 1970 A clear conception of the several features and of the construction of a typical compressor embodying the improvements and of the mode of operation thereof may be had by referring to the drawings accompanying and forming a part of this specification wherein like reference characters are used to designate the same or similar parts in the various views.

FIG. 1 is a part-sectional plan view of a typical screw compressor embodying the present invention;

FIG. 2 is a longitudinal section through the male rotor taken along the line 2-2 of FIG. 1;

FIG. 3 is a transverse section through the suction end of the compressor taken generally along the line 33 of FIG. 2;

FIG. 4 is a transverse section through the discharge end taken generally along the line 44 of FIG. 2;

FIG. 5 is a fragmentary transverse section taken along the line 55 of FIG. 2;

FIG. 6 is a fiat section through the slide valve taken along the arcuate line 66 of FIG. 5;

FIG. 7 is a similar section to that of FIG. 6 but showing a somewhat modified ported rotor;

FIG. 8 is a fragmentary longitudinal section through the suction end of a rotor provided with a control valve at such end;

FIG. 9 is a part-sectional view of another modification wherein the porting to exhaust is through the hollow vanes instead of through the rotor hubs; and

FIG. 10 is a transverse section through the female rotor of FIG. 9, the section having been taken along the line 1010.

DETAILED DESCRIPTION Referring to the drawings, the screw type rotary compressor shown therein comprises, in general, a stationary housing 16 having a working space therein formed by two intersecting bores 18, 20 having coplanar axes extending longitudinally through the casing, and a pair of complementary meshing rotors 22, 24 having shafts 26, 28 respectively rotatably journalled in the bores 18, 20 within the housing 16. In the embodiment shown, the rotor 22 has its shaft 26 extending outwardly through the end of the housing and adapted to be driven by an electric motor, gasoline engine or the like (not shown).

The housing, generally designated by numeral 16, comprises, more specifically, a central cylinder or casing portion 32 closed at opposite ends by removable end heads 34, 36, the casing and heads being provided in the usual manner with abutting flanges and suitable fasteners for securing the same in place. The intersecting parallel bores 18., 20 are formed in the central casing member 32, and these bores are in open communication with an inlet or suction port 38 opening substantially radially through the end head 34 into one end of the casing portion 32, and with a discharge port 40 opening substantially radially through the end head 36 and communicating with the opposite end of casing member 32.

The compressor operating means comprises generally the complementary helically threaded rotors 22, 24 rotatably journalled in the parallel bores 18, 20 respectively. As shown, the rotor 22 which, in this case, is the driven rotor, has four generally convex lobes or lands 42, and this rotor is commonly referred to as the male or the main rotor. The rotor 24 has six generally concave grooves 44 and is commonly referred to as the female or gate rotor. The extending ends of the rotor shaft 28 are rotatably journalled at their opposite ends in antifriction bearing assemblies 46, 48 housed in the end heads 34, 36 respectively, and the shaft of the rotor 24 is rotatably supported in like manner in anti-friction bearings.

In the compressor shown and described, a plurality of compression chambers are formed by the mating main rotor lobes or lands 42 and the gate rotor grooves 44, of which there are a greater number, as the rotors 22, 24 rotate in opposite directions and in approximate contact with the walls of the casing bores 18, 20. As the rotors rotate, the compression chambers sequentially open to their full volume and fill with gas while in communication with the inlet port 38. Thereafter, as the main rotor lobes 42 enter into the greater number of mating gate rotor grooves 44, the volume of gas contained in the compression chambers is progressively reduced by the shortening of the length of each chamber from its inlet to its discharge end. Thus, with a decrease in volume, the internal pressure in each chamber is progressively raised from inlet or suction pressure to discharge pressure. It is thereby apparent that the compression chambers are axially displaced toward the discharge port 40 and are sequentially brought into gasdelivering registration with the discharge port.

As the compressor thus operates, discharge high pressure gas is conducted from the compressor discharge port 40 to a receiver tank, not shown, by means of a suitable discharge pipe provided with the usual check valve to prevent back flow of receiver gas to the compressor whenever the compressor is completely unloaded or stopped. Since the receiver, discharge or high pressure pipe, and check valve are all wel known components in refrigeration and-like systems they have not been shown herein in detail.

As the rotors 22, 24 rotate as hereinabove described, gas is drawn into the interior of the compressor housing 16 through the intake or suction conduit 38 and past the intersecting arcuate inlet portions 52 formed in the end head 34. As the gas is thereafter compressed by the cooperating lobes 42 and mating grooves 44, the compressed high pressure gas is discharged through intersecting arcuate discharge ports 54 formed in the end head 36 from which the high pressure gas is conducted via discharge conduit 40 to the receiver as hereinabove described.

In accordance with the present invention, each of the rotor shafts 26, 28 is hollow to thereby provide exhaust chambers 58, 60 the by-pass or exhaust chambers 58, 60 communicating with spaces between the lobes or lands 42 through ports 62 and with the valleys 44 in the rotor 24 through ports 64. In addition, the chamber 58 is ported at its other end to the suction or intake passage as by way of ports 66, and passageway 68, and the chamber 60 being placed in communication with the intake or suction line via ports 70 and passageway 72.

Then, to control the capacity of the compressor to variable extents depending upon demand, the rotors 22, 24 are provided with annular undercut portions 76, 78 respectively at the end adjacent and surrounding the ports 62, 64, each of the undercut portions being provided with a cylindrical or tubular slide valve 80, 82 respectively extending from the respective undercut portions 76, 78 and into mating undercut portions in the end head 36. Each of the slide valves 80, 82 embraces the shafts of the respective rotors 22, 24 and is cut away as at 86 in FIGS. 6 and 7 so as to uncover or reveal the ports 62, 64 to a greater or lesser extent depending upon demand.

Each of the slide valves is constantly urged to open position as by means of a spring 88 or the like (see FIG. 2), and the outer end of each slide valve is exposed to fluid admitted under pressure to space 90 via port 92 and conduit 94 under control of a pair of solenoid valves '4 96, 98 which are responsive to the demand for compressed gas from the compressor.

Thus, whenever there is a demand for gas, the solenoid valves 96, 98 will be actuated to pressurize the space at the end of each of the slide valves, and the slide valves will thereby be actuated to the left as viewed in FIG. 2 to close the ports 62, 64, thereby causing the compressor to operate at full capacity. However, as the demand for gas decreases, the solenoid valves 96, 98 will be actuated to reduce the pressure Within the space 90 and cause the slide valves to be moved to the right by action of the springs 88 to thereby uncover more or less of the ports 62, 64 and thereby permit high pressure gas to be exhausted through these ports into the exhaust chambers 58, 60 and back to the suction or inlet side of the compressor.

While the invention has thus been shown as embodying slide valves on each of the rotors 22, 24 at the high pressure discharge ends thereof, similar slide valves can be incorporated at the inlet or suction end of one or both of the rotors as shown in FIG. 8. In this embodiment, the suction port is reduced in size, as shown, to thus prevent over pressurizing, and the shaft 28 is again shown as being hollow through at least part of its length to provide an exhaust chamber 104 which is ported at 106 to an undercut portion 108 in the rotor 24, the undercut portion 108 being, in turn, ported to the valleys via ports 110. Again, a cylindrical slide valve 112 is housed within the undercut portion 108 and within a similar mating undercut portion 114 in the end head 34, and the exhaust chamber 104 is similarly ported via ports 116 and passage 118 back to the intake or suction side of the compressor. The slide valve 112 is once again urged to a position uncovering the ports 106 as by means of a spring 120, and a pressurized line 122 responsive to demand for gas communicates through port 124 with the space 114 behind the slide valve 112. Thus, when there is a demand for high pressure fluid, the line 122, 124 is depressurized allowing springs to cause the valve 112 to shift to the left and completely uncover the ports 110 thereby causing the compressor to operate at capacity. Thus, the flow path after cutoff of the main suction port is into suction chamber and then thru 118, 116, 104, 106 and 110 into gate rotor grooves. However, as the demand decreases, the pressure in lines 122, 124 and in space 114 increases and the. valve 112 is shifted to the right, as viewed in FIG. 8, and the ports 106, 110 are thereby covered.

While the compressors in each of the embodiments hereinabove described are provided with a hollow shaft and with means for exhausting or unloading or intake or loading through one or the other end of the hollow shaft of one or both of the rotors, the invention can also be applied to a compressor having hollow lobes or lands as shown in FIGS. 9 and 10. As shown in this embodiment, one or both of the rotors have the lobes or lands thereof hollow as at 132 from one end of the rotor to the other. With specific regard to the embodiment of FIG. 8 wherein the control is at the suction end and the main suction port is of reduced size, several additional advantages are present as follows: Internal overpressurizing is avoided, control of the slide valve 112 by automatic means responsive to either suction or discharge pressures is possible, the pressure dilference across the slide valve 112 is also minimal, and the valve is of extremely simple and economical construction.

The hollow exhaust chamber 132 thus formed within the lobes or lands is ported through ports 134 to an undercut portion 136 at the discharge end of the rotor 130, and a tubular or cylindrical valve 138 is again housed within the undercut portion 136, the valve 138 having a porting portion 140 cut away from its forward end to uncover the ports 134 to a greater or lesser extent. The tubular valve 138 is again urged toward open position as by spring means 142, and the rear face of the tubular valve within space 144 is exposed to pressurized fluid via line 146 to a greater or lesser extent depending upon demand for gas flow to the system. Thus, during periods of increased demand, the high pressure fluid existing in conduit 146 will be such as to fully act upon the rear face of the tubular valve 138 and cause the same to move to the left against the pressure of the spring 142 and thereby close the ports 134 and 150, thus causing the compressor to deliver a full load. However, at times of reduced load, one or more of the ports 134 will be exposed to a greater or lesser extent by the valve 138 to ports 150 which vent the undercut area 136 to the space within the lobes or lands between the valleys 152 thereof so as to relieve the pressure existing within the valleys 152 to an extent depending upon the compressor demand. Thus, the hollow lobes or lands perform in the same manner as the hollow shaft to control the capacity of the compressor and to unload the same during periods of no demand.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

We claim:

1. A rotary compressor comprising, a housing provided with intersecting cylindrical rotor chambers and suction and discharge ports arranged in the rotor chamber walls near the opposite ends of said housing, a plurality of complementary helically threaded rotors rotatably supported within said rotor chambers and cooperating with each other and with the chamber walls to form pockets at the suction end of the rotors for receiving fluid through said suction port; the fluid being compressed as it is advanced axially by said pockets along said rotors from the suction end to the discharge end as the rotors are revolved with the compressed fluid being discharged through the discharge ports, means forming an exhaust chamber within the confines of said rotors, said exhaust chamber being communicable with said pockets and with the suction port, and valve means movable axially of said rotors for regulating flow of exhaust fluid from said pockets to the suction port through the exhaust chamber, whereby the capacity of the compressor is varied.

2. A rotary compressor according to claim 1, wherein the exhaust chamber is formed in the rotor shaft.

3. A rotary compressor according to claim 1, wherein the exhaust chamber is formed in the rotor threads.

4. A rotary compressor according to claim 1, wherein the valve for controlling flow of fluid through the exhaust chamber is tubular.

5. A rotary compressor according to claim 4, wherein the tubular valve is housed within an undercut portion of the rotor surrounding the rotor shaft.

6. A rotary compressor according to claim 5, wherein each of the rotors is undercut and houses a tubular valve adjacent its discharge end.

7. A rotary compressor according to claim 5, wherein each of the rotors is undercut and houses a tubular valve adjacent its suction end.

8. A rotary compressor according to claim 1, wherein the valve for controlling flow of fluid through the exhaust chamber is automatically responsive to demand for compressed fluid.

9. A rotary compressor according to claim 6, wherein the valve for controlling flow of fluid through the exhaust chamber is constantly resiliently urged to unloaded condition.

10. A rotary compressor according to claim 7, wherein the valve for controlling flow of fluid through the exhaust chamber is constantly resiliently urged to loaded condition.

References Cited UNITED STATES PATENTS 2,194,196 3/1940 Heinrich et al 230138 2,266,820 12/1941 Smith 230143 2,358,815 9/1944 Lysholm 230143 2,477,003 7/1949 Paget 230138 3,057,543 10/1962 Marsden 230143 3,088,659 5/1963 Nilsson et a1. 230l38 3,151,806 10/1964 Whitfield 230138 3,432,089 3/1969 Schibbye 230138 DONLEY J. STOCKING, Primary Examiner W. I. GOODLIN, Assistant Examiner US. Cl. X.R. 

